Microtubules have pivotal roles in fundamental cellular processes and are targets of antitubulin chemotherapeutics1. Microtubule-targeted agents such as Taxol and vincristine are prescribed widely for various malignancies, including ovarian and breast adenocarcinomas, non-small-cell lung cancer, leukaemias and lymphomas1. These agents arrest cells in mitosis and subsequently induce cell death through poorly defined mechanisms2. The strategies that resistant tumour cells use to evade death induced by antitubulin agents are also unclear2. Here we show that the pro-survival protein MCL1 (ref. 3) is a crucial regulator of apoptosis triggered by antitubulin chemotherapeutics. During mitotic arrest, MCL1 protein levels decline markedly, through a post-translational mechanism, potentiating cell death. Phosphorylation of MCL1 directs its interaction with the tumour-suppressor protein FBW7, which is the substrate-binding component of a ubiquitin ligase complex. The polyubiquitylation of MCL1 then targets it for proteasomal degradation. The degradation of MCL1 was blocked in patient-derived tumour cells that lacked FBW7 or had loss-of-function mutations in FBW7, conferring resistance to antitubulin agents and promoting chemotherapeutic-induced polyploidy. Additionally, primary tumour samples were enriched for FBW7 inactivation and elevated MCL1 levels, underscoring the prominent roles of these proteins in oncogenesis. Our findings suggest that profiling the FBW7 and MCL1 status of tumours, in terms of protein levels, messenger RNA levels and genetic status, could be useful to predict the response of patients to antitubulin chemotherapeutics.
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We thank P. Ekert for FDM cell lines, J. Stinson for sequencing assistance, S. Johnson and C. Santos for assistance with obtaining patient samples, P. Haverty for bioinformatics analysis, C. Grimaldi for cloning assistance, J. Dynek for TaqMan advice, D. French for tumour analysis, C. Quan and J. Tom for peptide synthesis, I. Zilberleyb and the Baculovirus Expression Group for cloning and protein production, S. Charuvu for generating MCL1 point mutants, A. Bruce for graphics assistance, the Genentech Cancer Genome Project Team, Z. Modrusan, R. Soriano and the microarray lab for ovarian tumour data sets, K. Newton for editorial assistance, W. Wei for sharing unpublished results, and A. Eldridge, D. Kirkpatrick, D. Vucic, E. Varfolomeev, T. Goncharov, A. Cochran, O. Huang, A. Huang, Y. Pereg, A. Loktev, D. Phillips, J. Wu, M. van Delft, D. Eaton, E. Shaulian, T. Hunter, S. Cory, J. Adams, A. Strasser, R. Deshaies and G. Evan for discussions. Work in the Huang laboratory is supported by the National Health and Medical Research Council (program grant #461221, IRIISS grant #361646 and a fellowship to D.C.S.H.), the Leukemia and Lymphoma Society (SCOR 7413), the National Institutes of Health (grants CA043540 and CA80188), the Australian Cancer Research Foundation, and an Australian Research Council Australian Postdoctoral fellowship to T.O. We apologize to our colleagues whose primary work could not be cited owing to space constraints.
The file contains Supplementary Figures 1-39 with legends, Supplementary Methods, additional references and Supplementary Tables 1-2.
This file contains a corrected version of Supplementary Figure S21 and legend. This file was uploaded on 21 November 2011.
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Frontiers in Oncology (2019)